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  • frequencies... frequencies.... frequency... network of stochastic oscillators... QUBIT... frequencies);
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  • qubits
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  • IEEE Transactions on Ultrasonics, FerroElectrics, and Frequency Control... oscillator
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  • IEEE Transactions on Ultrasonics, FerroElectrics, and Frequency Control... oscillator
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  • We analyze the coherent dynamics of a fluxonium device (Manucharyan et al 2009 Science 326 113) formed by a superconducting ring of Josephson junctions in which strong quantum phase fluctuations are localized exclusively on a single weak element. In such a system, quantum phase tunnelling by occurring at the weak element couples the states of the ring with supercurrents circulating in opposite directions, while the rest of the ring provides an intrinsic electromagnetic environment of the qubit. Taking into account the capacitive coupling between nearest neighbors and the capacitance to the ground, we show that the homogeneous part of the ring can sustain electrodynamic modes which couple to the two levels of the flux qubit. In particular, when the number of Josephson junctions is increased, several low-energy modes can have frequencies lower than the qubit frequency. This gives rise to a quasiperiodic dynamics, which manifests itself as a decay of oscillations between the two counterpropagating current states at short times, followed by oscillation-like revivals at later times. We analyze how the system approaches such a dynamics as the ring's length is increased and discuss possible experimental implications of this non-adiabatic regime.
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  • Since the dawn of quantum information science, laser-cooled trapped atomic ions have been one of the most compelling systems for the physical realization of a quantum computer. By applying qubit state dependent forces to the ions, their collective motional modes can be used as a bus to realize entangling quantum gates. Ultrafast state-dependent kicks [1] can provide a universal set of quantum logic operations, in conjunction with ultrafast single qubit rotations [2], which uses only ultrafast laser pulses. This may present a clearer route to scaling a trapped ion processor [3]. In addition to the role that spin-dependent kicks (SDKs) play in quantum computation, their utility in fundamental quantum mechanics research is also apparent. In this thesis, we present a set of experiments which demonstrate some of the principle properties of SDKs including ion motion independence (we demonstrate single ion thermometry from the ground state to near room temperature and the largest Schrodinger cat state ever created in an oscillator), high speed operations (compared with conventional atom-laser interactions), and multi-qubit entanglement operations with speed that is not fundamentally limited by the trap oscillation frequency. We also present a method to provide higher stability in the radial mode ion oscillation frequencies of a linear radiofrequency (rf) Paul trap--a crucial factor when performing operations on the rf-sensitive modes. Finally, we present the highest atomic position sensitivity measurement of an isolated atom to date of ~0.5 nm Hz^(-1/2) with a minimum uncertainty of 1.7 nm using a 0.6 numerical aperature (NA) lens system, along with a method to correct aberrations and a direct position measurement of ion micromotion (the inherent oscillations of an ion trapped in an oscillating rf field). This development could be used to directly image atom motion in the quantum regime, along with sensing forces at the yoctonewton [10^(-24) N)] scale for gravity sensing, and 3D imaging of atoms from static to higher frequency motion. These ultrafast atomic qubit manipulation tools demonstrate inherent advantages over conventional techniques, offering a fundamentally distinct regime of control and speed not previously achievable.
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  • 6-The electron oscillating period as functions of the temperature and the cyclotron frequency in triangular quantum dot qubit under an electric field.docx... Fig.4. A-Function relationship between the first excited state energy and the temperature and the electron-phonon coupling constant for different cyclotron frequencies and ,,,; B-Function relationship between the first excited energy and the temperature and the electric field strength for different cyclotron frequencies and ,,,; C-Function relationship between the first excited energy and the temperature and the confinement length for different cyclotron frequencies and ,,,; D-Function relationship between the first excited energy and of the temperature and the Coulomb impurity potential for different cyclotron frequencies and ,,,... Fig.1. A-Function relationship between the ground state energy and the temperature and the cyclotron frequency for different electron-phonon coupling constants and ,,, ; B-Function relationship between the ground state energy and the temperature and the cyclotron frequency for different electric field strengths and ,,,; C-Function relationship between the ground state energy and the temperature and the cyclotron frequency for different confinement lengths and ,,,; D-Function relationship between the ground state energy and the temperature and the cyclotron frequency for different Coulomb impurity potentials and ,,,... Fig.6. A-The electron oscillation period as functions of the temperature and the cyclotron frequency for different electron-phonon coupling constants and ,,,; B-The electron oscillation period as functions of the temperature and the cyclotron frequency for different electric field strengths and,,,; C-The electron oscillation period as functions of the temperature and the cyclotron frequency for different confinement lengths and ,,,; D-The electron oscillation period as functions of the temperature and the cyclotron frequency for different Coulomb impurity potentials and ,,,... 7-The electron oscillating period as functions of the temperature and the electron-phonon coupling constant and etc. in triangular quantum dot qubit under an electric field.docx... 2-The first excited state energy as functions of the temperature and the cyclotron frequency in triangular quantum dot qubit under an electric field.docx... 3-The ground state energy as functions of the temperature and the electron-phonon coupling constant and etc. in triangular quantum dot qubit under an electric field.docx... Fig.7. A-The electron oscillation period as functions of the temperature and the electron-phonon coupling constant for different cyclotron frequencies and ,,,; B-The electron oscillation period as functions of the temperature and the electric field strength for different cyclotron frequencies and ,,,; C-The electron oscillation period as functions of the temperature and the confinement length for different cyclotron frequencies and ,,,; D-The electron oscillation period as functions of the temperature and the Coulomb impurity potential for different cyclotron frequencies and ,,,... 1-The ground state energy as functions of the temperature and the cyclotron frequency in triangular quantum dot qubit under an electric field.docx... Fig.3. A-Function relationship between the ground state energy and the temperature and the electron-phonon coupling constant for different cyclotron frequencies and ,,,; B-Function relationship between the ground state energy and the temperature and the electric field strength for different cyclotron frequencies and ,,,; C-Function relationship between the ground state energy and of the temperature and the confinement length for different cyclotron frequencies and ,,,; D-Function relationship between the ground state energy and the temperature and the Coulomb impurity potential for different cyclotron frequencies and ,,,
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  • Superconducting qubits
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  • While the advanced coherent control of qubits is now routinely carried out in low frequency (GHz) systems like single spins, it is far more challenging to achieve for two-level systems in the optical domain. This is because the latter evolve typically in the THz range, calling for tools of ultrafast, coherent, nonlinear optics. Using four-wave mixing micro-spectroscopy, we here measure the optically driven Bloch vector dynamics of a single exciton confined in a semiconductor quantum dot. In a combined experimental and theoretical approach, we reveal the intrinsic Rabi oscillation dynamics by monitoring both central exciton quantities, i.e., its occupation and the microscopic coherence, as resolved by the four-wave mixing technique. In the frequency domain this oscillation generates the Autler-Townes splitting of the light-exciton dressed states, directly seen in the four-wave mixing spectra. We further demonstrate that the coupling to acoustic phonons strongly influences the FWM dynamics on the picosecond timescale, because it leads to transitions between the dressed states.
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  • While the advanced coherent control of qubits is now routinely carried out in low frequency (GHz) systems like single spins, it is far more challenging to achieve for two-level systems in the optical domain. This is because the latter evolve typically in the THz range, calling for tools of ultrafast, coherent, nonlinear optics. Using four-wave mixing micro-spectroscopy, we here measure the optically driven Bloch vector dynamics of a single exciton confined in a semiconductor quantum dot. In a combined experimental and theoretical approach, we reveal the intrinsic Rabi oscillation dynamics by monitoring both central exciton quantities, i.e., its occupation and the microscopic coherence, as resolved by the four-wave mixing technique. In the frequency domain this oscillation generates the Autler-Townes splitting of the light-exciton dressed states, directly seen in the four-wave mixing spectra. We further demonstrate that the coupling to acoustic phonons strongly influences the FWM dynamics on the picosecond timescale, because it leads to transitions between the dressed states.
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